Different types of orthopaedic appliances for bracing the joints of the human system are known. The primary purpose of such appliances or orthoses is to provide stability and support for a joint that has become mechanically unstable due to some form of pathology.
In the simplest form orthoses are known that substantially immobilize a joint so as to facilitate the healing of injured tissue. In more complex forms functional orthoses are known that attempt to restore normal or near normal stability and joint kinematics to a joint that has some form of residual laxity. Such appliances can also provide prophylaxis for repaired or reconstructed ligaments.
The mechanical designs of functional orthoses vary greatly. Orthoses can be either static or dynamic in design. Dynamic orthoses allow movement of a joint while they control excessive moment in order to protect the joint from further injury. A dynamic orthosis employs active restraint, or preload, to a joint for the purpose of resisting translation of the bones at the joint interface. A static orthosis rests passively on the limb until forces that tend to create instability occur.
The knee is one of the largest and most complex joints in the human system. It relies almost entirely on soft tissue structures in the form of ligaments, tendons, joint capsule and cartilage for mechanical stability. Because of its complexity and reliance on soft tissue for mechanical stability the knee is susceptible to injury.
The problem with bracing any joint is that the brace must be affixed on the skin. All designers and manufacturers of orthoses must operate under this constraint. Because of this limitation, little resistance is available in known orthoses with which to oppose tangential forces. In addition, the interposed soft tissue between an orthosis and the structures of a joint prevent a direct mechanical interface with the supporting structures of a limb. An important consideration in the design of any orthosis is the ability to effectively transfer load to the affected joint.
While many conventional orthoses have been developed for the knee complex, there are little if any orthoses specifically intended to brace the proximal tibiofibular joint. The reason for this is that the role of the proximal tibiofibular joint in pathologies of the knee and ankle has received little recognition in the medical literature.
The proximal tibiofibular joint is an arthrodial plane joint consisting of a tibial facet located on the posterolateral aspect of the rim of the tibial condoyle, and a fibular facet located on the medial proximal aspect of the fibula. The facets of the joint are oriented in the posteromedial plane. Translations of the facet of the proximal fibula with the facet of the proximal tibia in this plane are either posteromedial or anterolateral.
The anterior and posterior ligaments of the proximal tibiofibular joint act in a synergistic relationship to maintain translations and rotations of the head of the fibula with the lateral tibial facet within their normal range of motion. In this capacity, the anterior and posterior ligaments apply forces to the proximal fibula that are balanced when the joint is in a neutral position. The proximal tibiofibular joint is in a neutral position in weight bearing characterised by erect, quiet standing.
Other stabilizing structures of the proximal tibiofibular joint are: 1) the interossesus membrane which is comprised of a fibrous sheet running the length between the fibula and the tibia; 2) a strong fibrous capsule which surrounds the joint and is attached to the margins of the articular facets and the lateral collateral ligament, which in turn originates from the lateral epicondyle of the femur and inserts at the apex of the fibula; and 3) the biceps femoris muscle which in turn inserts on the apex of the fibula around the insertion of the lateral collateral ligament.
The anterior ligament of the proximal tibiofibular joint is comprised of short, thick fibrous bands that angle obliquely and superomedially from the anterior aspect of the head of the fibula to the anterior aspect of the lateral tibial condoyle. The posterior ligament is comprised of a single thin band that angles obliquely and superomedially from the posterior aspect of the fibula to the posterior aspect of the lateral tibial condoyle. Differences in the thickness and therefore, the relative strength of the anterior and posterior ligaments in combination with differences in the angles in which the ligaments are oriented relative to the plane of the facets of the proximal tibiofibular joint create asymmetric loading of the proximal tibiofibular joint. The weaker structure of the posterior ligament predisposes it to damage from the excessive force associated with knee flexion in weight bearing.
Ligaments are designated by their function: i.e. reinforcing ligaments for the joint capsule, restrictive ligaments to restrict joint movements or guiding ligaments for guiding joint movements. The anterior and posterior ligaments of the proximal tibiofibular joint provide both a stabilizing effect on the joint and a guiding effect on the joint arthrokinematics. The force applied by these ligaments guides the proximal tibiofibular joint in rotation and in the glide and translation that occurs during knee and ankle joint motion.
The normal translations of the proximal fibula at the proximal tibiofibular joint are anterolateral, posteromedial, superior and inferior glide. Recent evidence shows that the surfaces of the tibiofibular joint translate as much as 5 millimetres with each other in flexion and extension of the knee joint. The normal rotations of the fibula are internal or external.
One-sixth of body weight may be considered to be a static load applied to the fibula during weight bearing with the remaining five-sixths being borne by the tibia. The proximal to middle one third of the fibula has greater tensile strength than the femur. Therefore, in weight bearing the fibula acts to dissipate torsional stresses and direct compressive loads.
In weight bearing cases, the proximal tibiofibular joint translates anterolaterally with a lateral rotation of the torso with reference to the associated limb and posteromedially with medial rotation of the torso with reference to the associated limb. As the talocrural joint dorsiflexes as in a standing squat position, the proximal fibula translates superiorly and anterolaterally while rotating externally in relation to its neutral position. When rising up on the toes, the proximal fibula translates posteromedially and inferiorly, and rotates internally with plantarilexion of the talocrural joint.
In non-weight bearing cases, the proximal fibular head translates posteromedially with knee extension and anterolaterally with knee flexion. During dorsiflexion of the talocrural joint, the proximal fibula translates anterolaterally while rotating externally. During plantarflexion of the talocrural joint, the proximal fibular head translates posteromedially while rotating internally.
The distal tibiofibular joint moves in response to movement of the proximal fibula. Due to the articulation of the medial surface of the distal fibula with the talus, excessive movement due to ligament pathology in the form of laxity, or restricted movement will affect the talocrural joint. Positional faults in the proximal and/or distal fibula create undue strain on the anterior talofibular, calcanealfibular and posterior talofibular ligaments. This alters the arthrokinematics of the talocrural joint.
The common peroneal nerve passes posteriorly over the head of the proximal fibula. It gives off genicular branches; the lateral sural cutaneous nerve and the sural communicating nerve, which innervate the tibiofemoral joint and the proximal tibiofibular joint. The common peroneal nerve is the only nerve that attaches to a bone, in this case, the fibular head, via a retinaculum. The common peroneal nerve then divides into the superficial and deep peroneal nerves, which are motor nerves to the muscles of the foot and ankle. Oval apertures in the interossesus membrane allow for passage of the anterior tibial and peroneal vessels. Research has shown that an external force greater than 30 mm Hg applied to soft tissue structures will impede arteries, veins and the vaso vasorum of the peripheral nerve.
Studies have demonstrated surgery can often be avoided with effective early treatment of instability of a joint. Therefore, the comfort, effectiveness and ease of use of an orthosis play a significant role in the success or failure of any therapy.